Vibration damping rubber member and process of producing the same

ABSTRACT

A process of producing a vibration damping rubber member, wherein a rubber material A which enables the vibration damping rubber member to have a low degree of dynamic spring stiffness, a rubber material B which enables the vibration damping rubber member to have a high vibration damping effect, and a vulcanizing agent capable of vulcanizing only an unvulcanized mass of the rubber material B are evenly mixed together and heated to vulcanize the rubber material B dispersed as the fine particles in the rubber material A. A vulcanizing agent capable of vulcanizing the rubber material A is added, and a thus obtained mixture is formed into a desired shape and heated to vulcanize the rubber material A so that the formed vibration damping rubber member has an island-sea structure in which fine particles of the vulcanized rubber material B are dispersed as a dispersed phase in a matrix phase of the vulcanized rubber material A.

FIELD OF THE INVENTION

The present invention relates to a vibration damping rubber member and aprocess of producing the same, and more particularly to a vibrationdamping rubber member capable of exhibiting low dynamic stiffness andhigh vibration damping effect, and a process suitable for producing sucha vibration damping rubber member. The present invention is alsoconcerned with a process of producing a vibration damping rubber memberhaving an increased vibration damping effect, so as to reduce itsdynamic/static ratio of spring constant for thereby reducing the dynamicstiffness.

DISCUSSION OF THE RELATED ART

As well known, a vibration damping rubber member interposed between twomembers in a vibration transmitting system so as to connect the twomembers in a vibration damping fashion has been widely used in variousfields. For instance, the vibration damping rubber member is used onautomotive vehicles, as engine mounts, body mounts, member mounts,suspension bushings, and so on.

A vibration damping rubber member used in a vibration transmittingsystem involving different kinds of vibrations having differentfrequencies, for instance, typically, the vibration damping rubbermember as used on the automotive vehicles as described above, isgenerally required to exhibit vibration damping characteristics suitableto effectively damp those different kinds of vibrations. Described indetail, the vibration damping rubber member used on the automotivevehicles is generally required to exhibit a relatively low degree ofdynamic spring stiffness with respect to input vibrations havingcomparatively high frequencies of 100 Hz or higher, and to exhibit arelatively high damping effect with respect to input vibrations havingcomparatively low frequencies of about 10-20 Hz. In the presentinvention, the dynamic spring stiffness is defined by a dynamic/staticratio (Kd₁₀₀/Ks) of spring constant of the vibration damping rubbermember, which is a ratio of a dynamic spring constant Kd₁₀₀ to a staticspring constant Ks of the vibration damping rubber member. The dynamicspring constant Kd100 is obtained when it is subjected to vibration of100 Hz. The dynamic spring stiffness decreases with a decrease of thedynamic/static ratio Kd₁₀₀/Ks. On the other hand, the damping effect isdefined by a loss factor (tan δ) of the vibration damping rubber memberwhen it is subjected to vibration of 15 Hz. The damping effect increaseswith an increase of the loss factor tan δ.

For producing vibration damping rubbers structure having improvedvibration damping characteristics as represented by a reduced degree ofdynamic spring stiffness and an increased damping effect, variousstudies have been made to improve the material of the vibration dampingrubber member and the process of preparing a composition of thematerial. For example, there has been proposed to use natural rubbers(NR) which are suitable for reducing the dynamic spring stiffness of thevibration damping rubber members, and add a carbon black to the naturalrubbers, to increase the damping effect of the vibration damping rubbermembers. However, the known vibration damping rubber members accordingto those studies are by no means sufficiently satisfactory in terms ofthe required vibration damping characteristics.

Described more specifically, the mechanism by which the dynamic springstiffness of a vibration damping rubber member is reduced is based onbonding, binding or linking among the molecules of polymers of therubber composition, or bonding and binding between the polymer moleculesand reinforcing additives contained in the rubber composition. On theother hand, the mechanism by which the vibration damping effect isincreased is based on a friction among the polymer molecules or amongthe polymer molecules and the reinforcing additives. Therefore, thereare problems that increasing the vibration damping effect of thevibration damping rubber member will cause an increase of the dynamicspring stiffness, while reducing the dynamic spring stiffness will causea decrease of the vibration damping effect. There has not been availablea rubber composition which exhibits a sufficiently low degree of dynamicspring stiffness and a sufficiently high vibration damping effect, whichare two distinct characteristics not compatible with each other.

In the meantime, there have been proposed fluid-filled vibration dampingrubber members, as improvements in the construction rather than thematerial. Generally, such fluid-filled vibration damping rubber membersuse an elastic body formed of a rubber composition in which a pluralityof fluid chambers are formed in fluid communication with each otherthrough orifice passages (restricted fluid passages). These fluid-filledvibration damping rubber members are arranged to exhibit desiredvibration damping characteristics depending upon respective frequencybands of the input vibrations; on the basis of resonance of a fluidflowing through the orifice passages. Accordingly, those fluid-filledvibration damping rubber members are inevitably complicated inconstruction, with a relatively large number of components, and sufferfrom potential problems of a relatively high cost and considerabledifficulty of manufacture.

The vibration damping rubber members are required to have a relativelyhigh degree of hardness, in view of their applications in which therubbers should withstand a relatively large load, for instance. Thisrequirement is conventionally satisfied by using a rubber compositionwhich contains a diene-based rubber material such as a natural rubber(NR), and additives such as a carbon black. The addition of suchadditives including the carbon black makes it possible to increase thehardness and the vibration damping effect of the vibration dampingrubber member, but inevitably results in an undesirable increase in thedynamic spring stiffness. Various other approaches for improving therubber composition have been proposed to obtain a vibration dampingrubber member capable of exhibiting the desired characteristics, namely,low dynamic spring stiffness and high damping effect. For instance, thedamping effect is increased by adding a suitable rubber material to thenatural rubber (NR). However, the reduction of the dynamic/static ratioof spring constant of the vibration damping rubber members according tosuch approaches is not still satisfactory.

SUMMARY OF THE INVENTION

The present invention was made in view of the background art describedabove. It is a first object of this invention to provide a vibrationdamping rubber member which is capable of exhibiting both a low degreeof dynamic spring stiffness and a high vibration damping effect andwhich can be economically and easily produced, and a process suitablefor producing such a vibration damping rubber member.

The first object indicated above may be achieve according to the presentinvention, which provides a vibration damping rubber member having anisland-sea structure in which fine particles of a vulcanized rubbermaterial B which enables the vibration damping rubber member to have ahigh vibration damping effect are dispersed as a dispersed phase in amatrix phase of a vulcanized rubber material A that enables thevibration damping rubber member to exhibit a low degree of dynamicspring stiffness, the vibration damping rubber member beingcharacterized in that the vulcanized rubber material B functioning asthe dispersed phase is formed by vulcanizing an unvulcanized mass of therubber material B while the unvulcanized mass of the rubber material Bis evenly mixed with and dispersed in an unvulcanized mass of the rubbermaterial A, and the unvulcanized mass of the rubber material A isvulcanized while the vulcanized rubber material B is dispersed in theunvulcanized mass of the rubber material A.

The vibration damping rubber member constructed according to the presentinvention has an island-sea structure constituted by the matrix phaseconsisting of the vulcanized rubber material A which enables the dampingrubber member to exhibit a low degree of dynamic spring stiffness, andthe dispersed phase consisting of the vulcanized rubber material B whichenables the damping rubber member to have a high vibration dampingeffect. The present vibration damping rubber member is primarilycharacterized by this island-sea structure which is formed as describedabove. In the island-sea structure, the vulcanized rubber material Afunctioning as the matrix phase permits a significant reduction in thedynamic spring stiffness of the damping rubber member, while thevulcanized rubber material B evenly dispersed as fine particles in thematrix phase of the vulcanized rubber material A assures a highvibration damping effect of the damping rubber member.

In essence, the vulcanized rubber material A and the vulcanized rubbermaterial B in the present vibration damping rubber member caneffectively function, independently of each other, to reduce the dynamicspring stiffness and to increase the vibration damping effect,respectively, and at the same time, unlike the conventional rubbercomposition.

Accordingly, the present vibration damping rubber member can be suitablyused as vibration damping rubber structures for automotive vehicles, andother damping rubber structures in a vibration transmitting systeminvolving different kinds of vibrations having different frequencies,and is capable of effectively damping such vibrations.

In addition, the present vibration damping rubber member does notrequire such a complicated construction as provided in a fluid-filledvibration damping structure, and can therefore be produced economicallyand comparatively easily.

According to one preferred form of the vibration damping rubber memberof the invention, the vulcanized rubber material B consists of fineparticles which have an average size of 0.1-100 μm and which aredispersed in the vulcanized rubber material A. In this case, thevibration damping characteristics are further improved (the dynamicspring stiffness is further reduced, and the vibration damping effect isfurther increased), and the vibration damping rubber member is given thedesired physical properties.

According to another preferred form of the vibration damping rubbermember of the invention, the rubber material A consists of NR, or amixture of NR and BR or SBR, and the rubber material B consists ofhalogenated IIR, maleicacid-modified EPM, CR, carboxyl-modified NBR,CSM, CPE, FR or acrylic rubber. In this form of the invention, thevibration damping rubber member exhibits further improved vibrationdamping characteristics.

The present invention also provides a vibration damping rubber memberhaving an island-sea structure in which fine particles of a vulcanizedrubber material B which enables the vibration damping rubber member tohave a high vibration damping effect are dispersed as a dispersed phasein a matrix phase of a vulcanized rubber material A that enables thevibration damping rubber member to exhibit a low degree of dynamicspring stiffness, characterized in that the rubber material A is anatural rubber, while the rubber material B is an acrylic rubber, andthe rubber materials A and B are mixed together in a proportion of90/10-60/40 by weight, and that the vulcanized rubber material Bfunctioning as the dispersed phase is formed as fine particles having asize of 0.1-100 μm, by vulcanizing an unvulcanized mass of the rubbermaterial B while the unvulcanized mass of the rubber material B isevenly mixed with and dispersed in an unvulcanized mass of the rubbermaterial A, and the unvulcanized mass of the rubber material A isvulcanized while the vulcanized rubber material B is dispersed in theunvulcanized mass of the rubber material A.

In this vibration damping rubber member according to the presentinvention, a suitable amount of the vulcanized acrylic rubber whichenables the damping rubber member to have a high vibration dampingeffect is dispersed as a disperse phase in the form of fine particleshaving a size of 0.1-100 μm, in a matrix phase of the natural rubberwhich enables the damping rubber member to exhibit a low degree ofdynamic spring stiffness. Accordingly, the present vibration dampingrubber structure is capable of exhibiting excellent vibration dampingcharacteristics (low dynamic spring stiffness and high vibration dampingeffect). Further, the disperse phase consisting of the acrylic rubbereffectively functions to distribute or reduce the load which acts on thedamping rubber, so that the durability of the damping rubber member isaccordingly increased.

The present invention further provides a process of producing avibration damping rubber member, characterized by: evenly mixingtogether an unvulcanized rubber material A which enables the vibrationdamping rubber member to exhibit a low degree of dynamic springstiffness, an unvulcanized rubber material B which enables the vibrationdamping rubber member to have a high vibration damping effect, and avulcanizing agent capable of vulcanizing only the unvulcanized rubbermaterial B; heating a mixture of the unvulcanized rubber materials A andB and the vulcanizing agent, to vulcanize the unvulcanized rubbermaterial B such that fine particles of the vulcanized rubber material Bare dispersed in the unvulcanized rubber material A; adding to themixture a vulcanizing agent capable of vulcanizing the unvulcanizedrubber material A; and forming a thus obtained mixture into a desiredshape, and heating the formed mixture to vulcanize the unvulcanizedrubber material A, for obtaining the vibration damping rubber memberhaving an island-sea structure in which fine particles of the vulcanizedrubber material B are dispersed as a dispersed phase in a matrix phaseof the vulcanized rubber material A.

This process according to the present invention permits advantageousformation of the island-sea structure in which fine particles of thevulcanized rubber material B which enables the damping rubber member tohave a high vibration damping effect are evenly dispersed as a dispersedphase in a matrix phase (sea phase) of the vulcanized rubber material Awhich enables the damping rubber member to exhibit a low degree ofdynamic spring stiffness. Thus, the vibration damping rubber membercapable of exhibiting both low dynamic spring stiffness and highvibration damping effect can be advantageously produced.

The present method makes it possible to comparatively easily andeconomically produce the vibration damping rubber member havingexcellent damping characteristics as described above.

In one preferred form of the process of the present invention, theunvulcanized rubber material A is evenly mixed with the rubber materialB to which the vulcanizing agent capable of vulcanizing only theunvulcanized rubber material has been mixed with the unvulcanized rubbermaterial. In this instance, the time required to mix the rubber materialA, the rubber material B and the vulcanizing agent capable ofvulcanizing only the rubber material B can be effectively shortened, andthe rubber material B and the vulcanizing agent can be more evenly oruniformly dispersed within the rubber material A, so that the vibrationdamping effect of the damping rubber member can be further effectivelyincreased.

In another preferred form of the process of the invention, wherein theunvulcanized rubber material A is vulcanized by a sulfur-basedvulcanizing system, while the unvulcanized rubber material B isvulcanized by a resin-based vulcanizing system, a metal-oxide-basedvulcanizing system or an amine-based vulcanizing system. In thisprocess, the rubber materials A and B are vulcanized by the respectivedifferent vulcanizing systems, making it possible to permit the produceddamping rubber member to have the island-sea structure which exhibitsfurther improved vibration damping characteristics.

The present inventors considered the application of the above-indicatedisland-sea structure to a vibration damping rubber member which isformed of a diene-based rubber composition such as an NR-based rubbercomposition and which has a loss factor tan δ of at least 0.1. The lossfactor represents the damping effect with respect input vibrationshaving low frequencies (e.g., 15 Hz). The inventors found that the useof a rubber material of functional group-vulcanization type as thedispersed phase of the island-sea structure makes it possible to obtaina vibration damping rubber member whose dynamic/static ratio of springconstant is considerably lower than that of the vibration damping rubbermember formed solely of the vulcanized diene-based rubber composition.

Accordingly, the present invention which was made also on the basis ofthe above-indicating finding has a second object of reducing thedynamic/static ratio of spring constant of a vibration damping rubbermember which has a high vibration damping effect as represented by aloss factor tan δ of at least 0.1, in particular, providing a processsuitable for producing a vibration damping rubber member capable ofexhibiting both a high vibration damping effect and a low degree ofdynamic spring stiffness.

The second object indicated above may also be achieved according to thepresent invention, which provides a process of producing a vibrationdamping rubber member having a desired shape, and a low degree ofdynamic/static ratio of spring constant and a high vibration dampingeffect, by vulcanizing and forming a rubber composition which includes adiene-based rubber material as a rubber component and which enables thevulcanized and formed rubber composition to have a loss factor tan δ ofat least 0.1, characterized in that a portion of the diene-based rubbermaterial is replaced by not greater than 40% by weight of a rubbermaterial of functional group-vulcanization type per 100% by weight of atotal amount of these two rubber materials, and the two rubber materialsand a vulcanizing agent capable of vulcanizing only the rubber materialof functional group-vulcanization type are evenly mixed together to forma mixture, which is heated to vulcanize the rubber material offunctional group-vulcanization type such that fine particles of thevulcanized rubber material of functional group-vulcanization type aredispersed in the diene-based rubber material, and wherein a vulcanizingagent capable of vulcanizing the diene-based rubber material A is addedto the mixture, and a thus obtained mixture is formed into a desiredshape and heated to vulcanize the diene-based rubber material A, forobtaining the vibration damping rubber member such that the vibrationdamping rubber member has an islands-sea structure in which fineparticles of the rubber material of functional group-vulcanization typeare dispersed as a dispersed phase in a matrix phase of the diene-basedrubber material and which has the low degree of dynamic/static ratio ofspring constant.

In the present process of the invention of producing a vibration dampingrubber member using a diene-based rubber material which has a lossfactor tan δ of at least 0.1, a portion of the diene-based rubbermaterial is replaced by not greater than 40% by weight of the rubbermaterial of functional group-vulcanization type per 100% by weight of atotal amount of these two rubber materials, so that the vulcanizedrubber material of functional group-vulcanization type constitutes thedispersed phase of the island-sea structure. In the present process,this island-sea structure is formed as described above. Thedynamic/static ratio of spring constant of the vibration damping rubbermember produced according to this process is considerably lower thanthat of a vibration damping rubber member formed solely of thedine-based rubber material, with respect to input vibrations havingrelatively high frequencies.

According to the present process of the invention of producing avibration damping rubber member having low dynamic/static ratio ofspring constant and high damping effect, the produced damping rubbermember is given the island-sea structure, so that the vibration dampingcharacteristics of the damping rubber member are considerably improved(with reduced dynamic spring stiffness and increased vibration dampingeffect) than those of a vibration damping rubber structure formed of anintimate mixture of two rubber materials which respectively give desireddifferent characteristics. The island-sea structure is further effectiveto improve the other physical properties required by the vibrationdamping rubber member. Thus, the present process permits advantageousmanufacture of a vibration damping rubber member capable of exhibiting asignificantly reduced dynamic/static ratio of spring constant and a highvibration damping effect, as well as assuring various physicalproperties required by the vibration damping rubber member.

According to one preferred form of the present process, the rubbermaterial of functional group-vulcanization type is halogenated IIR. Theuse of the halogenated IIR further improves the vibration dampingcharacteristics of the damping rubber member, that is, further reduceddynamic spring stiffness and further increased vibration damping effect.

According to another preferred form of the present process, thevulcanized rubber material of functional group-vulcanization type isdispersed in the form of fine particles having an average size of0.1-100 μm in the vulcanized diene-based rubber material. In this case,the vibration damping characteristics and other required physicalproperties of the damping rubber member are further improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph indicating a relationship between a dynamic/staticratio of spring constant and a loss factor, which relationship wasobtained in Example 1.

FIG. 2 is a graph indicating a tensile strength and a breakingelongation at different values of blending ratio of natural rubber andchlorinated butyl rubber, which were obtained in Example 1.

FIG. 3 is a graph indicating a relationship between the dynamic/staticratio of spring constant and the loss factor tan δ, which relationshipwas obtained in Example 3.

DETAILED DESCRIPTION OF THE INVENTION

The vibration damping rubber member according to the present inventionas described above is formed using a rubber composition consisting of arubber material A for reducing the dynamic spring stiffness of thedamping rubber and a rubber composition B for increasing the dampingeffect. Described in detail, an unvulcanized mass of the rubber materialA and an unvulcanized mass of the rubber material B are initiallyuniformly kneaded or mixed together, such that the unvulcanized rubbermaterial B is dispersed in the form of fine particles in theunvulcanized rubber material A. Then, the rubber material B isvulcanized, and the rubber material A is subsequently vulcanized, sothat the vibration damping rubber member consisting of the vulcanizedrubber materials A and B is formed. This is a major feature of thepresent invention.

Namely, the vibration damping rubber member produced by the process ofthe present invention having the above-described feature is not astructure formed of an intimate mixture of the vulcanized rubbermaterials A and B, but is a so-called “island-sea” structure in whichfine particles of the vulcanized rubber material B are highly uniformlyor evenly dispersed as a dispersed or discontinuous phase in a matrixphase of the vulcanized rubber material A. In this island-sea structure,the matrix phase of the vulcanized rubber material A assures asufficiently low degree of dynamic spring stiffness of the dampingrubber member, while the dispersed phase of the vulcanized rubbermaterial B assures a sufficiently high vibration damping effect of thedamping rubber member.

In essence, the vulcanized rubber material A and the vulcanized rubbermaterial B of the vibration damping rubber member according to thisinvention have respective distinct functions of improving the dynamicspring stiffness characteristic and the vibration dampingcharacteristic, and are capable of achieving these two functions withhigh efficiency. In other words, the use of the vulcanized rubbermaterials A and B advantageously permits reduction of the dynamic springstiffness and increase of the vibration damping effect, which have beenincompatible with each other.

The rubber material A used as the matrix phase for the vibration dampingrubber member according to the present invention may be selected asneeded, depending upon the desired characteristics of the damping rubbermember, from among various known kinds of rubber material that permitseffective reduction of the dynamic spring stiffness with respect tovibrations of relatively high frequencies in particular, aftervulcanization of the rubber material. For instance, the rubber materialA may be selected from diene-based rubber materials such as naturalrubber (NR), isoprene rubber (IR), butadiene rubber (BR), stylenebutadiene rubber (SBR) and acrylonitrile butadiene rubber (NBR).Preferably, the rubber material A is selected according to the presentinvention, from among rubber materials (hereinafter referred to as“NR-based materials”) which include NR as an essential component, forexample, from among NR, mixtures of NR and BR, and mixtures of NR andSBR, in order to assure efficient reduction of the dynamic springstiffness of the vibration damping rubber member.

On the other hand, the rubber material B used as the dispersed phase isrequired to exhibit a high vibration damping effect with respect tovibrations of relatively low frequencies in particular, aftervulcanization of the rubber material, and is further required to bevulcanized with a vulcanizing system that is different to that of therubber material A. Accordingly, the rubber material B is selected asneeded, depending upon the desired characteristics of the damping rubbermember, from among various rubber materials which are known to beeffective to improve the vibration damping characteristic and whichsatisfies the above-indicated requirement regarding the vulcanizingsystem. Where the rubber material A is selected from among the NR-basedrubber materials as described above, for instance, the rubber material Bare particularly preferably selected from among: chlorinated butylrubbers such as halogenated butyl rubber (halogenated IIR);maleicacid-modified ethylene propylene rubber (maleicacid-modified EPM);chloroprene rubber (CR); carboxyl-modified nitrile rubber(carboxyl-modified NBR); chlorosulfonated polyethylene (CSM);fluororubber (FR); chlorinated polyethylene (CPE); and acrylic rubber.The rubber materials B indicated above by way of example are alleffective to reduce the dynamic spring stiffness after thevulcanization, and can be vulcanized with a vulcanizing system differentfrom that of the NR-based rubber materials, as described below. Further,those rubber materials B permit effective improvements of variouscharacteristics of the vibration damping structure, such as gaspermeability resistance, weather resistance, heat resistance, ozoneresistance, chemical resistance, and durability, as indicated in thefollowing Table 1. Even where those rubber materials B have a structurein which cross linking of functional groups takes place, such rubbermaterials B are recognized as rubber materials of functionalgroup-vulcanization type.

TABLE 1 Rubber Material B Given Characteristics Halogenated IIR Gaspermeability resistance Maleicacid-modified Resistances to weather, heatand EPM ozone CR Resistances to heat, oil, ozone and gas permeabilityCarboxyl-modified Resistances to oil, gas permeability, NBR heat andozone CSM Resistances to weather, ozone, chemicals, heat and gaspermeability, and durability FR Resistances to heat, oil, chemicals, gaspermeability, and durability Acrylic rubber Resistances to weather,heat, oil, ozone and gas permeability, and durability CPE Durability andozone resistance

Acrylic rubber used as the rubber material A may be selected as needed,depending upon the desired characteristics of the damping rubber member,from among any known synthetic rubber materials whose major component isacrylic acid alkyl ester. In particular, it is preferable to use acrylicrubber materials which can be vulcanized with an amine-based vulcanizingsystem which will be described. For instance, it is preferable to use acopolymer (ACM) of acrylic acid alkyl ester and 2-chloroethyl vinylether, a copolymer (ANM) of acrylic acid alkyl ester and acrylonitrile,and a copolymer of acrylic acid alkyl ester and ethylene. The use ofsuch acrylic rubber materials advantageously permits an increase of thedurability of the vibration damping rubber member.

The process of producing a vibration damping rubber member having a lowdynamic/static ratio of spring constant and a high vibration dampingeffect according to the present invention is applied to a rubbercomposition whose major component is a diene-based rubber material(rubber material A), which is a rubber composition that gives avulcanized rubber mass having a loss factor tan δ of at least 0.1. Theuse of the rubber material A that gives a vulcanized rubber mass havinga loss factor tan δ of less than 0.1 does not reduce the dynamic/staticratio of spring constant of the produced damping rubber member to thedesired extent, even if the produced damping rubber member has an“island-sea” structure. To assure the desired characteristics of theproduced damping rubber member, it is desirable that the vulcanizedrubber mass indicated above have a JIS-A hardness value of at least A40,preferably, at least A50. If the hardness of the vulcanized rubber massobtained from the rubber material A is considerably low, the producedvibration damping rubber member cannot satisfy the requirement of itsapplicability.

The contents of appropriate known additives selected as needed, such asan oil as well as a carbon black generally added as a reinforcing agentare suitably determined so as to prepare the desired rubber compositionthat realizes the desired characteristics (tan δ≧0.1) of the produceddamping rubber member.

In the present invention, the vibration damping rubber member having theintended island-sea structure is produced using the unvulcanized rubbermaterials A and B which have been described above. To this end, theunvulcanized rubber material A and the unvulcanized rubber material Bare uniformly kneaded under heat, together with a vulcanizing agent(hereinafter referred to as “vulcanizing agent B”) which does notvulcanize the rubber material A but promotes the vulcanization of onlythe rubber material B. In this manner, the rubber material B can bevulcanized without the vulcanization of the rubber material A, whilefine particles of the unvulcanized rubber material B are evenlydispersed in the unvulcanized rubber material A.

The vulcanizing agent B used for vulcanizing the rubber material B isrequired to vulcanize only the rubber material B while holding therubber material A in the unvulcanized state, as described above.Accordingly, the vulcanizing agent B is selected as needed, dependingupon the specific rubber materials A and B, from among various knownvulcanizing agents that satisfy the above-indicated requirement.Described in detail, where the rubber material A is the NR-basedmaterial, the vulcanizing agent B is preferably selected, depending uponthe specific rubber material B, from among the following materialsindicated in the following TABLE 2, which do not vulcanize the NR-basedrubber material A: resins such as alkyl phenol resin and modifiedalkylphenol resin; metal oxides such as zinc oxide and magnesium oxide;and polyamines such as hexamethylenediamine carbamate. The rubbermaterial B is preferably vulcanized with a resin-based vulcanizingsystem, a metal-oxide-based vulcanizing system or an amine-basedvulcanizing system, which includes any one of those preferredvulcanizing agents B. It is noted that TABLE 2 lists the preferredvulcanizing agents B suitable for use with halogenated IIR,maleicacid-modified EPM, CR, carboxyl-modified NBR, CSM, FR, CPE andacrylic rubbers, which are preferably used as the rubber material A, asdescribed above.

TABLE 2 Rubber Vulcanizing Vulcanizing Vulcanization Promot- Material BSystem Agent B ing Agent/Aid Halogenated Resin Alkyl phenol4,4′-dithiodimorpholine IR Tellurium diethyldithio carbamate ResinModifed Zinc oxide alkylphenol resin Metal oxide Zinc oxide Zincdiethyldithio- carbamate Maleicacid- Metal oxide Zinc oxide modified EPMCR Metal oxide Zinc oxide 2-mercaptoimidazoline Magnesium oxideCarboxyl- Metal oxide Zinc oxide modified NBR CSM Metal oxide MagnesiumPentaerythritol oxide Dipentamethylene thiuram tetrasulfide FR Metaloxide Magnesium Calcium hydroxide oxide Acrylic Amine HexamethyleneDiorthotolyl rubber diamine guanidine carbamate CPE Metal oxideMagnesium Hexamethylene oxide dicarbamate

In the present invention, the rubber material B may be vulcanized with avulcanizing system consisting of the vulcanizing agent B and at leastone selected vulcanization promoting agent and/or aid which does notvulcanize the rubber material A. The appropriate vulcanization promotingagent(s) and/or aid(s) is/are selected depending upon the specificrubber material B and the specific vulcanizing agent B, as indicated inTABLE 2. The unvulcanized rubber materials A and B are kneaded togetherwith the vulcanizing agent B and the selected at least one vulcanizationpromoting agent and/or aid, so that the rubber material B is vulcanizedwith an improved result. Any other suitable additives known in the artfor rubber compositions may be added to the unvulcanized rubbermaterials A and B to provide a mixture thereof by kneading, providedthose additives do not vulcanize the rubber material A.

To promote the vulcanizing reaction of the rubber material B while theunvulcanized rubber materials A and B are evenly kneaded under heat,together with the vulcanizing agent B and other additives, the suitableamounts of the unvulcanized rubber materials A and B, the vulcanizingagent B and the selected additive(s) are introduced into a suitableknown kneader or mixer such as banbury mixer which permits kneading ormixing of polymer materials under an ordinary heating condition. Theamounts of the unvulcanized rubber materials A and B to be introducedinto the kneader are determined so that the vibration damping rubbermember to be formed as the end product can exhibit the desired operatingcharacteristics or physical properties. Generally, the ratio of theweight of the unvulcanized rubber material A to that of the unvulcanizedrubber material B is selected within a range between 95/5 and 30/70. Ifthe amount of the unvulcanized rubber material B is excessively smallerthan that of the unvulcanized rubber material B, the desired vibrationdamping effect of the produced damping rubber member cannot be obtainedowing to the vulcanized rubber material B. If the amount of theunvulcanized rubber material B is excessively larger than that of theunvulcanized rubber material A, on the other hand, the physicalproperties such as the tensile property and hardness of the vibrationdamping rubber member may be deteriorated. To assure the desiredphysical properties of the damping rubber member by preventing a risk ofdeterioration of the physical properties where the amount of the rubbermaterial B is larger than that of the rubber material A, the ratio ofthe weight of the rubber material A to that of the rubber material B ispreferably selected within a range between 95/5 and 50/50. Where theacrylic rubber is used as the rubber material B, however, theabove-indicated ratio by weight of the rubber materials A and B isdesirable selected within a range between 90/10 and 60/40. When theamount of the acrylic rubber used is smaller than the lower limitdetermined by the lower limit of this ratio by weight, the acrylicrubber does not permit sufficient improvements in the vibration dampingeffect and durability of the produced damping rubber member. When theamount of the acrylic rubber used is larger than the upper limitdetermined by the upper limit of the ratio by weight, on the other hand,the acrylic rubber may cause deterioration of the other physicalproperties, such as an increase in the permanent compressive strain.

In the process of this invention of producing the vibration dampingrubber member having a low dynamic/static ratio of spring constant and ahigh vibration damping effect, the maximum amount of the rubber materialB is 40% by weight of the total amount of the rubber materials A and B.If the amount of the rubber material B is more than 40% by weight, thedynamic/static ratio of spring constant of the produced vibrationdamping rubber member cannot be made sufficiently low, and there is arisk of deterioration of the physical properties of the damping rubbermember, such as insufficient hardness and considerable reduction of thetensile property, although the damping rubber member exhibits asufficiently high vibration damping effect.

The amounts of the vulcanizing agent B and the vulcanization promotingagent(s) and/or aid(s) which are introduced into the kneader togetherwith the unvulcanized rubber materials A and B are suitably determineddepending upon the amount of the unvulcanized rubber material B, inorder to permit the desired vulcanizing reaction of the rubber materialB.

The unvulcanized rubber materials A and B, the vulcanizing agent B andthe appropriate additive or additives may be simultaneously introducedinto the kneader or mixer, without any problem. However, it is desirableto prepare a mixture of the unvulcanized rubber material B, vulcanizingagent B and additive or additives, with a suitable proportion, in theform of a master batch, for example. In this case, the prepared mixtureand the rubber material A are introduced into the kneader, so as toestablish the desired ratio by weight of the unvulcanized rubbermaterials A and B. This method is effective to shorten the time requiredfor kneading or mixing the materials within the kneader, and permitimproved uniformity or evenness of dispersion of the rubber material B,vulcanizing agent B and additive(s) in the rubber material A, therebyassuring a considerable increase in the vibration damping effect of thedamping rubber member owing to the vulcanized rubber material B.

The materials which have been introduced into the kneader as describedabove are subsequently kneaded so that the rubber material B is dividedinto fine particles small enough to assure the desired characteristicsof the produced damping rubber member, and until the fine particles aredispersed in the rubber material A evenly enough to assure the desiredcharacteristics. To this end, the kneading time is generally determinedas needed, in view of the specific kinds and the amounts of the rubbermaterials A and B and the operating characteristics of the kneader, inorder to establish the desired state of dispersion of the fine particlesof the rubber material B. The materials are kneaded at a temperaturethat facilitates the kneading operation and permits a high degree ofvulcanizing reaction of the unvulcanized rubber material B.

As a result of the kneading operation under heat, the vulcanized rubbermaterial B is evenly dispersed in the form of fine particles in theunvulcanized rubber material A. The particle size of the vulcanizedrubber material B is determined as needed, depending upon the specificconditions of kneading as described above, in order to assure thedesired vibration damping effect. The average particle size of thevulcanized rubber material B is selected generally within a range of0.1-100 μm, and preferably within a range of 0.1-30 μm. If the averageparticle size is excessively small, the produced vibration dampingrubber member does not exhibit the desired damping effect. If theaverage particle size is excessively large, the physical properties ofthe produced vibration damping rubber member are adversely influenced.The particle size of the vulcanized rubber material B may be measured byvarious known methods. Preferably, the particles of the vulcanizedrubber material B are observed by a scanning electron microscope (SEM)or a scanning probe microscope (SPM), to measure the sizes of theparticles and determine the average particle size.

After the vulcanization of the unvulcanized rubber material B asdescribed above, a vulcanizing agent (hereinafter referred to as“vulcanizing agent A”) capable of vulcanizing the unvulcanized rubbermaterial A within which the vulcanized rubber material B is dispersed isadded to the rubber material A, to vulcanize the unvulcanized rubbermaterial A into the desired vibration damping rubber member.

In the production of the vibration damping rubber member according tothe present invention, the vulcanizing agent A to be added to vulcanizethe unvulcanized rubber material A may be selected from among variousknow vulcanizing agents, depending upon the specific rubber material Aand the desired characteristics of the produced rubber member, providedthe vulcanizing agent A permits effective promotion of the vulcanizingreaction of the rubber material A. The amount of the vulcanizing agent Ais suitably determined depending upon the amount of the rubber materialA used. Where the rubber material A is an NR-based rubber material asdescribed above, a sulfur-based vulcanizing agent containing sulfur ispreferably used as the vulcanizing agent A for vulcanizing the rubbermaterial A.

In the present process, suitable vulcanization promoting agents and/oraids may be used with the vulcanizing agent A, to prepare a vulcanizingsystem for vulcanizing the rubber material A. Typical examples of thevulcanization promoting agents include: sulfenamides such asN-tert-butyl-2-benzothiazolylsulfenamide (BBS), N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), andN-oxydiethylene-2-benzothiazolylsulfenamide (OBS); dithiocarbamates suchas zinc dimethyldithiocarbamate (ZnMD C), and zincdiethyldithiocarbamate (ZnEDC); and thiurams such as tetramethyl thiuramdisulfide (TMTD), tetraethyl thiuram disulfide (TETD), and tetrabutylthiuram disulfide (TBTD). Typical vulcanization promoting aids includezinc oxide and stearic acid.

Various other suitable additives used for rubber materials may be addedto the unvulcanized rubber material A, as needed. Those additives mayinclude: reinforcing agents such as carbon black; products of reactionbetween acetone and diphenylamine; phenylenediamines such asN-phenyl-N′-isopropyl-p-phenylenediamine; anti-aging agents such as wax;and softening agents such as process oil and mineral oil. Needless tosay, these additives should not prevent the produced damping rubbermember from exhibiting the desired property of low dynamic springstiffness, and the amounts of the additives should be determined so asnot to deteriorate this property. For instance, the use of carbon blackin an excessively large amount will have a considerable influence on thedynamic spring stiffness of the rubber material A. In this respect, thecarbon black is preferably used in an amount of not larger than 60 partsby weight per 100 parts by weight of the rubber material A.

To mix the vulcanizing agent A and the various additives indicated abovewith the rubber material A within which the vulcanized rubber material Bis dispersed, the vulcanizing agent A and the additives are added to therubber material A, and these components are evenly kneaded or mixedtogether by a suitable kneader or mixer, for instance, by a mixer ofroll type, so that the unvulcanized rubber material A can be uniformlyvulcanized in a desired manner, in a vulcanizing step following theaddition of the vulcanizing agent A and additives. The kneading ormixing length of time and the temperature condition in which thekneading is effect are suitably selected.

After the vulcanizing agent A and additives are added to the rubbermaterial A, the obtained rubber composition is formed into the desiredvibration damping rubber member, with the unvulcanized rubber material Abeing vulcanized, as indicated above. To this end, the rubbercomposition is formed into a desired shape, by a suitable molding methodusing a molding die, for instance, at the suitably determinedtemperature at which the unvulcanized rubber material A is vulcanized.It is preferable to form the damping rubber member, by a press-moldingand -vulcanizing process in which the molding and the vulcanization areeffected concurrently. The vulcanizing conditions such as thetemperature, pressure and time may be determined as needed, dependingupon the specific kinds of the rubber material A, vulcanizing agent Aand additives, so as to vulcanize the rubber material A as desired. Thevibration damping rubber member to be produced as a result of themolding and vulcanization of the rubber material A as described abovemay be provided with a metallic structure made of a ferrous or aluminummaterial, which may be bonded to the rubber member during or after themolding and vulcanizing operation. In this respect, it is to beunderstood that the process of the present invention is applicable tonot only a vibration damping rubber member without such a metallicstructure, but also a vibration damping rubber member with such ametallic structure bonded thereto. It is also to be understood that theconfiguration and size of the damping rubber member to be produced byvulcanizing the rubber material A are not particularly limited, but maybe determined as needed, depending upon the desired characteristics andapplication of the damping rubber member.

In essence, the vibration damping rubber member to be produced accordingto the present invention has an “island-sea” structure in which in whichfine particles (generally of a size within a range of 0.1-100 μm) of thevulcanized rubber material B are evenly dispersed as a dispersed ordiscontinuous phase in a matrix or continuous phase of the vulcanizedrubber material A. This island-sea structure permits the damping rubbermember to exhibit both of a sufficiently low degree of dynamic springstiffness and a sufficiently high vibration damping effect. In otherwords, the process of the present invention permits easy and economicalproduction of a comparatively simple vibration damping rubber member,using the selected rubber materials A and B, so as to enable thevibration damping rubber member to exhibit improved vibration dampingcharacteristics, that is, low dynamic spring stiffness and highvibration damping effect.

Thus, the process of the present invention can be advantageously used toform the vibration damping rubber member highly capable of dealing withdifferent kinds of input vibrations having different frequency bands, bysuitably selecting the rubber composition including the rubber materialsA and B, depending upon the frequency bands of the input vibrations, sothat the selected rubber composition permits the produced vibrationdamping rubber member to exhibit low dynamic spring stiffness and highdamping effect with respect to the specific kinds of input vibrations tobe damped. The thus produced vibration damping rubber member can besuitably used so as to exhibit excellent vibration dampingcharacteristics, in a vibration transmitting system as in an automotivevehicle, which involves different kinds of vibrations to be damped.

EXAMPLES

Several examples of the present invention will be described to furtherclarify the present invention. It is to be understood that the presentinvention is by no means limited to these examples, and that theinvention may be embodied with various changes, modifications andimprovements, other than the following examples and the details of theforegoing descriptions, which may occur to those skilled in the art,without departing from the spirit of this invention.

Example 1

(1) Dynamic Characteristics Test, Tensile Test and Hardness Test

Initially, an unvulcanized natural rubber (NR) was prepared according tothe present invention, as the rubber material A which enables theproduced vibration damping rubber member to exhibit a sufficiently lowdegree of dynamic spring stiffness, and there was prepared alsoaccording to the present invention a master batch of a compositionindicated in TABLE 3 below, which includes a mixture of unvulcanizedchlorinated butyl rubber (Cl-IIR) as the rubber material B which enablesthe produced vibration damping rubber member to exhibit a sufficientlyhigh vibration damping effect, and zinc oxide as the vulcanizing agentB. The master batch further includes zinc diethyldithiocarbamate (ZnEDC)as the vulcanization promoting agent, and stearic acid as thevulcanization promoting aid.

TABLE 3 Composition Contents (by weight) Chlorinated IIR 100 Zinc oxide1.5 ZnEDC 1.5 Stearic acid 1

Precursors of Samples 1-6 according to the present invention wereprepared from respective combinations of the NR and master batchcomposition prepared as described above, which combinations haverespective proportions of mixing or blending (by weight) of the NR andCl-IIR (blending ratios of NR/Cl-IIR) as indicated in TABLE 4 below. Theindividual combinations were introduced into a kneader called “banburymixer”, and were evenly kneaded or mixed together for 5-10 minutes at atemperature of 150-160° C., so that only the rubber material B in theform of Cl-IIR was vulcanized, without vulcanization of the NR. For eachprecursor of Samples 1-7, the sizes of particles of Cl-IIR dispersedwithin the mass of the NR were measured to obtain the average particlesize of Cl-IIR. The obtained average particle size of Cl-IIR in theprecursor of each sample was confirmed to be about 0.5-5 μm.

To 100 parts by weight of the unvulcanized NR in the precursor of eachSample, there were added sulfur as the vulcanizing agent A and variousadditives indicated in TABLE 4, in respective amounts indicated in TABLE4. These components were evenly kneaded with a mixer of roll type, andthe obtained mixtures were subjected to a press-molding and -vulcanizingprocess for 20 minutes at 160° C., to prepare vulcanized rubber membersas test pieces of Samples 1-6 according to the present invention, forperforming a dynamic characteristics test, a tensile test and a hardnesstest.

Of the additives to be added to the NR as indicated in TABLE 4,N-cyclohexyl-2-benzothiazyl sulfenamide (CBS) was used as thevulcanization promoting agent, while zinc oxide and stearic acid wereused as the vulcanization promoting aids. In the present Example 1,N-phenyl-N′-isopropyl-p-phenylenediamine was used as the anti-agingagent, and carbon black was used as the reinforcing agent, while mineraloil was used as the softening agent.

The test pieces to be used for the dynamic characteristics test arecylindrical pieces formed of the vulcanized rubber and having a diameterof 50 mm and a height dimension of 25 mm. To the upper and lower facesof these cylindrical test pieces, there are bonded with a bonding agenta pair of circular iron plates having a diameter of 60 mm and athickness of 6 mm. The test pieces to be used for the tensile test aredumb-bell-shaped test pieces (No. 3 type) formed of the vulcanizedrubber according to JIS-K-6251-1993, “Tensile Test Method of VulcanizedRubber”. The test pieces to be used for the hardness test are platesformed of the vulcanized rubber having a thickness of 2 mm according toJIS-K-6253-1997, “durometer hardness test” described in “Physical TestMethod of Vulcanized Rubber”.

TABLE 4 Samples of the Invention 1 2 3 4 5 6 NR/Cl-IIR Ratio 90/10 85/1570/30 50/50 40/60 30/70 Vulcanizing Agent A and Additives (parts byweight)* Sulfur 2 2 2 2 2 2 CBS 1 1 1 1 1 1 Zinc oxide 5 5 5 5 5 5Stearic acid 2 2 2 2 2 2 Anti-aging agent 5 5 5 5 5 5 Carbon black 40 4040 40 40 40 Mineral oil 10 10 10 10 10 10 *Parts by weight per 100 partsby weight of NR

On the other hand, test pieces according to Comparative Samples 1 and 2,which are similar to the test pieces according to Samples 1-6 of thepresent invention, were prepared for the dynamic characteristics test,tensile test and hardness test, by molding and vulcanizing respectiverubber compositions indicated in TABLE 5, for 20 minutes at atemperature of 160° C., by a press-molding and -vulcanizing process.These rubber compositions include only the unvulcanized NR as the rubbermaterial.

The functions of the additives to be added to the NR in the ComparativeSamples are the same as those in Samples 1-6 of the present inventiondescribed above. In Comparative Sample 2, the carbon black is used in acomparatively large amount, and therefore also functions to improve thevibration damping effect, as in the known damping rubber members.

TABLE 5 Comparative Samples 1 2 Components (parts by weight) NR 100 100Sulfur 2 2 CBS 1 1 Zinc oxide 5 5 Stearic acid 2 2 Anti-aging agent 5 5Carbon black 40 85 Mineral oil 10 10

The test pieces according to Samples 1-6 of the present invention andthe test pieces according to Comparative Samples 1 and 2, which wereprepared as described above, were subjected to the dynamiccharacteristics test, tensile test and hardness test in the followingmanners.

Dynamic Characteristics Test

An axial load was applied to each test piece until the test piece wascompressed by an axial distance of 5.5 mm. After the load was oncereduced, the load was increased to compress the test piece again by theaxial distance of 5.5 mm. During this second load application, a changeof the amount of compressive strain of each test piece with an increaseof the load was measured, to obtain a load-strain curve. Load values P₁and P₂ (unit: N) when the amount of compressive strain was 1.25 mm and3.75 mm were obtained from the obtained load-strain curve. A staticspring constant Ks (N/mm) of each test piece was calculated according tothe following equation:Ks=(P ₂ −P ₁)/2.5

Further, each test piece was compressed by an axial distance of 2.5 mm.In this compressed state, the test piece was subjected at its lower endto harmonic compressive vibration having a frequency of 100 Hz such thatthe amplitude of the vibratile displacement at the middle of the axiallength of the 2.5 mm-compressed test piece was held constant at ±0.05mm. A dynamic spring constant (storage spring constant) Kd₁₀₀ (N/mm) ofthe test piece subjected to the 100 Hz vibration was obtained accordingto JIS-K-6385-1995, (a) non-resonance method described in “Test Methodof Vibration Damping Rubber”. On the basis of the thus obtained dynamicspring constant Kd₁₀₀ and the static spring constant Ks indicated above,a dynamic/static ratio (Kd₁₀₀/Ks) of spring constant of each test piecewas calculated. The calculated dynamic/static ratio values of the testpieces are indicated in TABLE 6 and TABLE 7. It is noted that thedynamic spring stiffness of the test piece when it is subjected to the100 Hz vibration decreases with a decrease of the dynamic/static ratio(Kd100/Ks) of spring constant.

In the dynamic characteristics test in Example 1, each test piece wasagain compressed by an axial distance of 2.5 mm. In this compressedstate, the test piece was subjected at its lower end to harmoniccompressive vibration having a frequency of 15 Hz such that theamplitude of the vibratile displacement at the middle of the axiallength of the 2.5 mm-compressed test piece was held constant at ±0.5 mm.A loss factor tan δ of the test piece subjected to the 15 Hz vibrationwas obtained according to JIS-K-6385-1995, (a) non-resonance methoddescribed in “Test Method of Vibration Damping Rubber”. The obtainedvalues of the loss factor tan δ are also indicated in TABLE 6 and TABLE7. It is noted that the vibration damping effect of the test pieceincreases when it is subjected to the 15 Hz vibration with an increaseof the loss factor.

A relationship between the dynamic/static ratio Kd₁₀₀/Ks and the lossfactor tan δ[15 Hz] of each test piece is indicated in the graph of FIG.1. In the graph, “□” represents the test pieces according to Samples 1-6of the present invention, while “●” represents the test pieces accordingto Comparative Samples 1 and 2.

Tensile Test

The test pieces for the tensile test were subjected to a tensile loadwith a tensile tester, according to JIS-K-6251-1993, until each testpiece was broken or fractured. In this process of application of thetensile load to the test piece, there were measured a tensile stress(100% modulus) when the test piece had 100% elongation, a maximumtensile stress (tensile strength Tb) when the test piece was broken, andan amount of elongation (breaking elongation Eb) when the test piece wasbroken. The measurements are indicated in TABLE 6 and TABLE 7. Thetensile strength Tb and the breaking elongation Eb of the test piecesaccording to Samples 1-6 of this invention are indicated in respectivebar and line graphs of FIG. 2, in relation to the ratio of blending ofthe NR and Cl-IIR indicated in TABLE 4. The tensile strength Tb and thebreaking elongation Eb of the test piece according to Comparative Sample1 is indicated in the graphs of FIG. 2, at the position of the blendingratio of 100/0.

Hardness Test

The hardness of each test piece for the hardness test was measured by atype-A durometer, according to JIS-KK-6253-1997, “durometer hardnesstest” described above. The measurements are indicated in TABLE 6 andTABLE 7, as JIS-A Hardness.

TABLE 6 Samples of the Invention 1 2 3 4 5 6 Dynamic CharacteristicsTest Dynamic/static 1.51 1.51 1.81 2.15 2.30 2.45 ratio (Kd₁₀₀/ Ks) Lossfactor 0.094 0.120 0.217 0.260 0.310 0.362 tanδ [15 Hz] Tensile Test100% modulus 1.4 1.4 1.3 1.4 1.3 1.3 (Mpa) Tensile 22.6 19.3 18.6 14.610.0 5.6 strength Tb (Mpa) Breaking 600 580 500 440 390 350 elongationEb (%) JIS-A Hardness A48 A47 A48 A47 A47 A47

TABLE 7 Comparative Samples 1 2 Dynamic Characteristics TestDynamic/static ratio Kd₁₀₀/Ks 1.51 1.51 Loss factor tan δ [15 Hz] 0.0940.120 Tensile Test 100% modulus (Mpa) 1.4 1.4 Tensile strength Tb (Mpa)22.6 19.3 Breaking elongation Eb (%) 600 580 JIS-A Hardness A48 A47

It will be understood from TABLES 6 and 7 and FIG. 1 that the test pieceaccording to Comparative Sample 1 using only the NR as the rubbermaterial has a low degree of dynamic spring stiffness (lowdynamic/static ratio of spring constant), but also has a low vibrationdamping effect (low loss factor), while the test piece according toComparative Sample 2 formed of the composition including a larger amountof carbon black mixed with the NR than the test piece according toComparative Sample 1 has a higher vibration damping effect that the testpiece according to Comparative Sample 1, but has a considerably highdegree of dynamic spring stiffness, as indicated in the graph of FIG. 1.Accordingly, it will be easily predicted that the use of carbon black ina much larger amount than in Comparative Sample 2 in an attempt tofurther increase the vibration damping effect, as in the prior art, doesnot realize a sufficiently low degree of dynamic spring stiffness, as isapparent from broken line in FIG. 1. Therefore, such prior art methodcannot be said to be effective.

To the contrary, it is recognized that each of the test pieces accordingto Samples 1-6 of the present invention permits an effective increase inthe vibration damping effect (loss factor), while maintaining a lowdegree of dynamic spring stiffness (dynamic/static ratio of springconstant), unlike the test piece according to Comparative Sample 2. Itwill therefore be understood that the present invention is significantlyeffective to realize the desired vibration damping characteristics,namely, both of a low degree of dynamic spring constant and a highvibration damping effect.

It will also be understood from the results of the tensile and hardnesstests indicated in TABLES 6 and 7 and in FIG. 2 that most of the testpieces according to Samples 1-6 of the present invention exhibit tensileand hardness characteristics such as the 100% modulus, tensile strengthTb and breaking elongation Eb, which are comparable with those of thetest pieces according to Comparative Samples 1 and 2. In particular, itwill be understood from the graphs in FIG. 2 that the physicalproperties such as the tensile strength Tb and breaking elongation Ebcan be maintained at sufficiently high values, provided the amount ofthe Cl-IIR used as the rubber material B is smaller than that of the NRused as the rubber material A.

(2) Durability Test

As in the tests described above, an unvulcanized natural rubber (NR) wasprepared as the rubber material A which enables the produced vibrationdamping rubber member to exhibit a sufficiently low degree of dynamicspring stiffness, and there was prepared a master batch (hereinafterreferred to as “master batch AEM) of a composition indicated in TABLE 8below, which includes a mixture of unvulcanized acrylic rubber (AEM:VAMAC-G available from Mitsui Dupont Polychemical Kabushiki Kaisha) asthe rubber material B which enables the produced vibration dampingrubber member to exhibit a sufficiently high vibration damping effect,and hexamethylenediamine carbamate as the vulcanizing agent B. Themaster batch AEM further includes diorthotolyl guanidine (DT) as thevulcanization promoting agent, and stearic acid as the vulcanizationpromoting aid.

TABLE 8 Composition Contents (by weight) Acrylic rubber 100Hexamethylenediamine carbamate 2 DT 5 Stearic acid 2

Precursors of Samples 7-9 according to the present invention and aprecursor of Comparative Sample 4 were prepared from respectivecombinations of the NR and master batch AEM prepared as described above,which combinations have respective proportions of mixing or blending (byweight) of the NR and AEM (blending ratios of NR/AEM) as indicated inTABLE 9 below. The individual combinations were introduced into akneader called “banbury mixer”, and were evenly kneaded or mixedtogether for 5-10 minutes at a temperature of 150-160° C., so that onlythe acrylic rubber was vulcanized, without vulcanization of the NR.

To the precursors of Samples 7-9 of the invention and the precursors ofComparative Samples 3 and 4 (Comparative Sample 3 prepared from only theunvulcanized NR), there were added sulfur and various additivesindicated in TABLE 9, in respective amounts indicated in TABLE 9. Theadditives consist of zinc oxide plus stearic acid, HAF carbon black(ASTM-N330), and a softening agent in the form of an aromatic processoil. All components indicated above were evenly kneaded with a mixer ofroll type, and the obtained mixtures were subjected to a press-moldingand -vulcanizing process, to prepare vulcanized rubber members as testpieces of Samples 7-9 according to the present invention and ComparativeSamples 3 and 4, for performing a durability test and a permanentcompressive strain test. The vulcanization was effected for 20 minutesat a temperature of 160° C. for the test pieces to be used for thedurability test, and for 30 minutes at 160° C. for the test pieces to beused for the permanent compressive strain test. For each of the testpieces according to Samples 7-9 of the invention, the sizes of particlesof the acrylic rubber dispersed within the mass of the NR were measuredto obtain the average particle size of the acrylic rubber. The obtainedaverage particle size of the acrylic rubber in each test piece wasconfirmed to be about 0.5-3 μm.

The test pieces to be used for the durability test are dumb-bell-shapedtest pieces (No. 5 type) formed according to JIS-K-6251-1993, “TensileTest Method of Vulcanized Rubber”. The test pieces to be used for thepermanent compressive strain test are large pieces according toJIS-K-6262-1997, “Permanent Strain Test Method of Vulcanized Rubber andThermoplastic Rubber”.

TABLE 9 Comparative Samples of the Invention Samples 7 8 9 3 4Components (parts by weight) NR 60 80 90 100 50 Master Batch AEM 43.621.8 10.9 — 54.5 Carbon Black 25 25 25 25 25 Softening Agent 5 5 5 5 5Sulfur 1 1 1 1 1 CBS 2 2 2 2 2 Zinc oxide + 5 5 5 5 5 Stearic Acid

The test pieces according to Samples 7-9 of the invention andComparative Samples 3-4, which were prepared as described above, weresubjected to the durability test and the permanent compressive straintest in the following manners:

Durability Test

Each of the test pieces for the durability test was repeatedly subjectedto a tensile load by a suitable tensile tester, so as to cause the testpiece to undergo a tensile strain of 0-100% 300 times per minute, untilthe test piece was broken or fractured. The number of times of thetensile strain until the test piece was broken was obtained. Theobtained numbers of times are indicated in TABLE 10, as the valueindicative of the durability (dumb-bell fatigue) of the test pieces.

Permanent Compressive Strain Test

Each of the test pieces for the permanent compressive strain test washeld compressed at a predetermined compression ratio, and at 100° C. for22 hours, with a suitable compressing device, by a method according toJIS-K-6262-1997, “5. Permanent Compressive Strain Test”. Then, thecompressive load was removed from each test piece, and the test piecewas held at the room temperature for a predetermined cooling time. Then,the thickness of a central portion of each test piece was measured toobtain the permanent compressive strain percentage. The obtainedpermanent compressive strain percentage values of the test pieces areindicated in TABLE 10.

TABLE 10 Samples of the Comparative Invention Samples 7 8 9 3 4Durability: Dumb-bell 10 7.0 6.5 5.0 12 Fatigue (× 10K) PermanentCompressive 38 34 33 33 48 Strain (%)

It will be apparent from the test result indicated in TABLE 10 that eachof the test pieces according to Samples 7-9 of the invention, which wereprepared from the natural rubber as the rubber material A for reducingthe dynamic spring stiffness, and the acrylic rubber as the rubbermaterial B for increasing the vibration damping effect, has asignificantly higher degree of durability than the test piece accordingto Comparative Sample 4 prepared from only the NR. The test pieceaccording to Comparative Sample 4 was prepared using the acrylic rubberas the rubber material B for increasing the vibration damping effect,but the content of the acrylic rubber is smaller than required by thepresent invention, so that the permanent compressive strain percentageof this test piece is higher than desired, although the durability ofthe test piece is improved. While the vibration damping rubber member isrequired to exhibit a low permanent compressive strain percentage, thisphysical property is deteriorated according to Comparative Sample 4.

Example 2

In this Example, an unvulcanized natural rubber (NR) or an unvulcanizedstylene butadiene rubber (SBR) was prepared as the rubber material A,while various mater batches were prepared as the rubber material B, byusing unvulcanized respective masses of fluororubber (FR), chloroprenerubber (CR), chlorosulfonated polyethylene (CSM), maleicacid-modifiednitrile rubber (X-NBR), copolymer (AEM) of acrylic acid alkyl ester andethylene, and chlorinated polyethylene (CPE), in combination of selectedadditives in respective proportions as indicated in TABLES 11 and 12.

TABLE 11 Unit: Parts by weight FR Master Batch CR Master Batch CSMMaster Batch FR 100 CR 100 CSM 100 MgO 3 MgO 4 MgO 5 CaO 6 ZnO 5Cross-linking aid²⁾ 3 Stearic acid 1 Vulcanization 2 promoting agent³⁾Vulcanization 0.5 promoting agent¹⁾ ¹⁾2-mercaptoimidazoline²⁾Pentaerythritol ³⁾Dipentamethylene thiuram tetrasulfide

TABLE 12 Unit: Parts by weight CPE X-NBR Master Batch AEM Master BatchMaster Batch X-NBR 100 AEM 100 CPE 100 Stearic acid 1 Stearic acid 2 MgO10 ZnO 1.5 Cross-linking 2 Plasticizer⁶⁾ 10 agent⁴⁾ Vulcanization 1.5Vulcanization 5 Cross-linking 3 promoting promoting agent⁴⁾ agent³⁾agent⁵⁾ ³⁾See TABLE 11. ⁴⁾Hexamethylenediamine carbamate ⁵⁾Diorthotolylguanidine ⁶⁾Dioctyl phthalate

Precursors of Samples 10-17 according to the present invention andComparative Samples 5-7 were prepared from respective combinations ofthe rubber material A and the master batch composition including therubber material B, which combinations have respective proportions ofmixing or blending (by weight) of the rubber materials A and B asindicated in TABLES 13 and 14 below. The individual combinations wereevenly kneaded or mixed together for 5-10 minutes at a temperature of150-160° C., so that only the rubber material B was vulcanized, withoutvulcanization of the rubber material A. For the precursor of each ofSamples 10-17, the sizes of particles of the rubber material B dispersedwithin the rubber material A were measured to obtain the averageparticle size of the rubber material B. The obtained average particlesize of the rubber material B in the precursor of each sample wasconfirmed to be about 0.5-5 μm.

In each preliminary sample thus prepared, the unvulcanized rubbermaterial A was vulcanized. Described in detail, 100 parts by weight ofthe unvulcanized rubber material A in each of the Comparative Sample 5and the Samples 10-14 of the invention was mixed with 2 parts by weightof sulfur as the vulcanizing agent A, 5 parts by weight of processingaid, and 1 part by weight of sulfenamide-based vulcanization promotingagent. These components were evenly kneaded, and the obtained mixtureswere subjected to a press-molding and -vulcanizing process for 20minutes at 160° C., as in Example 1, to prepare test pieces ofComparative Sample 5 and Samples 10-14 of the invention. For ComparativeSamples 6 and 7 and Samples 15-17 of the invention, 100 parts by weightof the unvulcanized rubber material A was mixed with 3 parts by weightof sulfur as the vulcanizing agent A, 5 parts by weight of processingaid, 25 parts by weight of HAF carbon black (ASTMN330), 10 parts byweight of softening agent (aromatic process oil), and 1 part by weightof sulfenamide-based vulcanization promoting agent. These componentswere evenly kneaded, and the rubber material A in each of the obtainedmixtures was subjected to a press-molding and -vulcanizing process for20 minutes at 160° C., to prepare test pieces of Comparative Samples 6and 7 and Samples 15-17 of the invention.

The thus obtained test pieces according to Comparative Samples andSamples of the invention were tested by the same methods as in Example1, to measure their tensile strength (Tb), breaking elongation (Eb) andJIS-A hardness, and also an amount of change (ΔTb) of the tensilestrength and an amount of change (ΔEb) of the breaking elongation aftera thermal aging test of the test pieces (at 80° C. for 250 hours).Further, the test pieces were subjected to the dumb-bell fatigue test,in the same manner as in Example 1. The results of the tests of the testpieces are indicated in TABLES 13 and 14. The test pieces were furthermeasured of their resistances to ozone and gas permeability. Themeasurements are also indicated in TABLES 13 and 14.

The resistance to ozone was evaluated by static ozone-deterioration testaccording to JIS-K-6301-1995. Described in detail, JIS No. 1 test pieceswere held elongated by 20% and exposed to an atmosphere having an ozoneconcentration of 50±5 pphm at 40° C., for 168 hours. The ozoneresistance was evaluated depending upon whether each test piece wasfractured or broken during its elongation and exposure to the atmosphereindicated above. The resistance to gas permeability was evaluated by amethod according to ASTM-D-1434-82. Namely, each test piece in the formof a 2 mm-thick sheet was exposed to a pressure difference on itsopposite sides at a temperature of 60° C. such that a pressure of 100Kpa of N₂ gas on one side (high-pressure side) of the sheet while 1330Pa acts on the other side (low-pressure side). The gas permeabilityresistance was evaluated on the basis of a rate (cc·cm/cm²·sec·atm) atwhich the N₂ gas permeates through the sheet from the high-pressure sideto the low-pressure side.

TABLE 13 Compar- ative Samples of the Invention Sample 5 10 11 12 13 14Polymer NR NR/FR NR/CR NR/ NR/ NR/ CSM X-NBR AEM Mixing Ratio 100 70/3070/30 70/30 70/30 30/70 Tb (MPa) 23 19 22 23 12 23 Eb (%) 690 860 840680 720 740 JIS-A A40 A38 A38 A42 A41 A43 Hardness After Thermal Aging:ΔTb (%) −22 −34 −31 −21 −12 −16 ΔEb (%) −11 −30 −56 −13 −6 −4Durabllity: 6 16 — 17 3 30 Dumb-bell fatigue (×10K) Gas permea- 2.652.34 2.00 1.92 2.00 2.30 bility (×10⁻⁹) (cc · cm/ cm² · sec) Ozonedeter- 72H — 120H — 144H Not ioration Broken hours

TABLE 14 Comparative Samples Samples of the Invention 6 7 15 16 17Polymer NR SBR NR/CPE SBR/CSM SBR/CPE Mixing Ratio 100 100 65/35 65/3565/35 Tb (MPa) 25 19 17 12 17 Eb (%) 630 670 670 270 590 JIS-A HardnessA50 A53 A58 A65 A65 After Thermal Aging: ΔTb (%) −41 −48 −55 0 −8 ΔEb(%) −24 −54 −52 −26 −32 Durability: 9 28 18 2 30 Dumb-bell fatigue(×10K) Ozone deterio- 14H 72H Not 96H 144H ration hours Broken

It will be understood from the results of the tests indicated in TABLES13 and 14 that the vulcanized rubber members according to Samples 10-17of the present invention prepared from the combinations of the polymersmixed together are excellent in the following characteristics,respectively:

-   -   Sample 10: Durability    -   Sample 11: Durability, and ozone resistance    -   Sample 12: Heat resistance, durability, gas permeability        resistance, and ozone resistance    -   Sample 13: Heat resistance, gas permeability resistance, and        ozone resistance    -   Sample 14: Heat resistance, durability, and ozone resistance    -   Sample 15: Durability, and ozone resistance    -   Sample 16: Heat resistance, and ozone resistance    -   Sample 17: Heat resistance, durability, and ozone resistance

Example 3

Precursors of Comparative Sample 11 and Samples 18 and 19 of the presentinvention were prepared from respective combinations of unvulcanizednatural rubber (NR) and/or unvulcanized stylene butadiene rubber (SBR)as the rubber material A, and master batch Cl-IIR prepared in Example 1.The individual combinations have respective proportions of mixing orblending (by weight) of the NR, SBR and Cl-IIR as indicated in TABLE 15below. The components of each combination were introduced into a kneadercalled “banbury mixer”, and were evenly kneaded or mixed together for5-10 minutes at a temperature of 150-160° C., so that only the rubbermaterial B in the form of Cl-IIR was vulcanized, without vulcanizationof the rubber material A. For each precursor of Samples 1-7, the sizesof particles of Cl-IIR dispersed within the mass of the rubber materialA were measured to obtain the average particle size of Cl-IIR. Theobtained average particle size of Cl-IIR in the precursor of each samplewas confirmed to be about 0.5-5 μm.

To 100 parts by weight of the unvulcanized rubber material A in theprecursor of each Sample, there were added sulfur as the vulcanizingagent A and various additives indicated in TABLE 15, in respectiveamounts indicated in TABLE 15. These components were evenly kneaded witha mixer of roll type, and the obtained mixtures were subjected to apress-molding and -vulcanizing process for 20 minutes at 160° C., toprepare test pieces of Samples 18 and 19 of the present invention andComparative Sample 11, for performing a dynamic characteristics test, ahardness test and a tensile test.

Of the additives to be added to the rubber material A as indicated inTABLE 15, N-cyclohexyl-2-benzothiazyl sulfenamide (CBS) was used as thevulcanization promoting agent, while zinc oxide and stearic acid wereused as the vulcanization promoting aids. In the present Example 3, waxwas used as the anti-aging agent, and carbon black was used as therubber characteristic adjusting agent (reinforcing agent), while an oilwas used as the softening agent.

TABLE 15 Samples of the Invention Comparative Samples 18 19 8 9 10 11 NR85 55 100 60 100 85 SBR — 35 — 40 — — Master batch 15 10 — — — 15 Cl-IIRSulfur 2 2 2 2 2 2 Stearic acid 5 5 5 5 5 5 Zinc oxide 2 2 2 2 2 2 Wax 22 2 2 2 2 Carbon black 55 50 55 50 40 40 Oil 5 25 5 25 10 10Vulcanization 2 2 2 2 2 2 promoting agent

Test pieces according to Comparative Samples 8, 9 and 10 were preparedby using only the rubber materials A which are respectively used inSamples 18 and 19 of the invention and Comparative Sample 11 and whichserve as the matrix phase (“sea” phase). Namely, these test pieces donot include the rubber material B dispersed in the rubber material Aaccording to the present invention. The test pieces according toComparative Samples 8, 9 and 10 include additives as also indicated inTABLE 15. The mixtures of the rubber material A and the additives weresubjected to a press-vulcanizing and -molding process at 160° C. for 20minutes, to obtain the test pieces. It will be understood from TABLE 15that Comparative Sample 8 is similar to a vulcanized rubber member ofSample 18 except that the rubber material B in the form of Cl-IIR is notdispersed in the rubber material A in the form of the NR. In the samesense, Comparative Sample 9 corresponds to Sample 19 of the invention,while Comparative Sample 10 corresponds to Comparative Sample 11.

The test pieces according to Samples 18 and 19 of the invention andComparative Samples 8-11 were subjected to the dynamic characteristicstest, hardness test and tensile test, in the same manner as inExample 1. The results of the tests are indicated in TABLE 16.

Relationships between the dynamic/static ratio (Kd₁₀₀/Ks) of springconstant and the loss factor tan δ [15 Hz] of the test pieces areindicated in the graph of FIG. 3, wherein “□” represents the test piecesaccording to Samples 18 and 19 of the present invention which have the“island-sea” structure, while “▪” represents the test piece according toComparative Sample 8 which has the “island-sea” structure but the matrixphase of which does not permit damping rubber characteristics asrequired by the present invention, while “●” represents the test piecesaccording to Samples 18 and 19 of the invention and Comparative Sample11 which do not include any amount of the rubber material B that givesthe “islands” phase.

TABLE 16 Samples of the Invention Comparative Samples 18 19 8 9 10 11Dynamic Characteristics Test Dynamic/static ratio 2.38 2.18 2.80 2.481.30 1.53 (Kd100/Ks) Loss factor tan δ[15 Hz] 0.189 0.178 0.175 0.1450.068 0.120 Physical Properties JIS-A hardness A65 A51 A65 A50 A50 A51Tensile strength 20 15 26 21 25 19 Tb (Mpa) Breaking elongation 480 530580 680 600 540 Eb (%)

It will be apparent from the results of the dynamic characteristics testindicated in TABLE 16 and FIG. 3 that the test piece according toComparative Sample 11 which uses Cl-IIR as the rubber material offunctional group-vulcanization type to give an “island-sea” structure tothe vulcanized rubber member of Comparative Sample 10 whose rubbercharacteristics do not meet the requirements of the present invention(i.e., tan δ=0.068<0.1) has a higher degree of vibration damping effect(i.e., higher loss factor tan δ) than the test piece according toComparative Sample 10, but has a relatively high dynamic/static ratio ofspring constant. Thus, it will be understood that the test piece springconstant. Thus, it will be understood that the test piece according toComparative Sample 11 does not solve the prior art problem that anincrease in the vibration damping effect will cause an increase in thedynamic/static ratio of spring constant.

It will also be understood that unlike the test piece according toComparative Sample 11, the test pieces according to Samples 18 and 19 ofthe present invention has a significantly increased loss factor tan andan effectively reduced dynamic/static ratio of spring constant, ascompared with the test pieces according to Comparative Samples 8 and 9the rubber material of which consists solely of the rubber material A.Namely, Samples 18 and 19 of the invention permit both a furtherimprovement in the vibration damping effect with respect tolow-frequency input vibrations, and a low dynamic/static ratio of springconstant (a low degree of dynamic spring stiffness) with respect tohigh-frequency input vibrations.

It will also be understood from the results of the hardness and tensiletests indicated in TABLE 16 that Samples 18 and 19 of this inventionassure the JIS-A hardness of at least A50, and are satisfactory in theother physical properties such as the tensile strength (Tb) and breakingelongation (Eb).

INDUSTRIAL APPLICABILITY

It will be understood from the foregoing description that the vibrationdamping rubber member according to the present invention is capable ofexhibiting both a low degree of dynamic spring stiffness and a highvibration damping effect, and can be suitably used as vibration dampingrubber members for automotive vehicles, such as an engine mount, andvarious other vibration damping structures which are required todifferent vibration damping characteristics depending upon differentkinds of input vibrations having different frequencies. The process ofproducing the vibration damping rubber member according to thisinvention permits economical and easy manufacture of vibration dampingrubber members having excellent damping characteristics.

The process of the invention permits the produced vibration dampingrubber member to exhibit a significantly reduced dynamic/static ratio ofspring constant while maintaining a high vibration damping effect, aswell as assure various physical properties required by the vibrationdamping rubber member. Thus, the present process has made it possible toproduce a vibration damping rubber member capable of exhibiting a highvibration damping effect and a low degree of dynamic spring constant.

1. A process of producing a vibration damping rubber member,characterized by: evenly mixing together an unvulcanized rubber materialA which enables the vibration damping rubber member to exhibit a lowdegree of dynamic spring stiffness, an unvulcanized rubber material Bwhich enables the vibration damping rubber member to have a highvibration damping effect, and a vulcanizing agent capable of vulcanizingonly said unvulcanized rubber material B; heating a mixture of saidunvulcanized rubber materials A and B and said vulcanizing agent, tovulcanize said unvulcanized rubber material B such that fine particlesof the vulcanized rubber material B, having an average size of 0.1 to100 μm, are dispersed in said unvulcanized rubber material A; adding tosaid mixture a vulcanizing agent capable of vulcanizing saidunvulcanized rubber material A; and forming a thus obtained mixture intoa desired shape, and heating the formed mixture to vulcanize saidunvulcanized rubber material A, for obtaining said vibration dampingrubber member having an island-sea structure in which fine particles ofthe vulcanized rubber material B are dispersed as a dispersed phase in amatrix phase of the vulcanized rubber material A.
 2. A process accordingto claim 1, wherein said unvulcanized rubber material A is evenly mixedwith the unvulcanized rubber material B to which said vulcanizing agentcapable of vulcanizing only said unvulcanized rubber material B has beenmixed with said unvulcanized rubber material.
 3. A process according toclaim 2, wherein said unvulcanized rubber material A is vulcanized by asulfur-based vulcanizing system, while said unvulcanized rubber materialB is vulcanized by a resin-based vulcanizing system, a metal-oxide-basedvulcanizing system or an amine-based vulcanizing system.
 4. A processaccording to claim 1, wherein said unvulcanized rubber material A isvulcanized by a sulfur-based vulcanizing system, while said unvulcanizedrubber material B is vulcanized by a resin-based vulcanizing system, ametal-oxide-based vulcanizing system or an amine-based vulcanizingsystem.
 5. A process according to claim 1, wherein said rubber materialA comprises NR or a mixture of NR and SBR, and said rubber material Bcomprises maleicacid-modified EPM, CSM, CPE, FR or acrylic rubber.
 6. Aprocess according to claim 1, wherein said rubber material A comprises amixture of NR and BR, and said rubber material B comprises halogenated II R, maleicacid-modified EPM, CR, carboxyl-modified NBR, CSM, CPE, FR oracrylic rubber.
 7. A process according to claim 1, wherein said rubbermaterial A comprises NR and said rubber material B comprises halogenatedI I R.